Disc drive machines record and reproduce information stored on a recording media. Conventional Winchester-type disc drives include a plurality of vertically-aligned, rotating information storage discs, each having at least one associated magnetic head that is adapted to transfer information between the disc and an external computer system. The information storage discs are journaled about a spindle motor assembly capable of rotating the discs at high speeds. The heads are carried by a plurality of vertically-aligned, elongated flexure arms that in turn are carried by a head positioner assembly. The head positioner assembly is adapted to move the heads back and forth in unison across the face of the vertically-aligned, elongated flexure arms that in turn are carried by a head positioner assembly. The head positioner assembly is adapted to move the heads back and forth in unison across the face of the vertically-aligned discs. The head positioner assembly are traditionally either rotationally mounted, or take the form of a carriage that is free to move back and forth along a single axis. In either case, the head positioner assembly is adapted to precisely position the heads relative to the magnetic information storage discs.
The spindle motor assembly includes a rotatable spindle hub that is carried by a fixed spindle shaft securely mounted to the housing. A plurality of information storage discs are journaled about the spindle hub. Spacer discs are provided between adjacent information storage discs. The vertically aligned information storage discs are clamped to the spindle hub by a disc clamp secured by a plurality of screws.
In practice, the disc clamp design is quite critical to high performance disc drives and there are several design criteria that must be met in order to provide an effective disc clamp. Specifically, the disc clamp must provide a uniform clamping force along its clamping surface to avoid such problems as top disc distortion. The clamp must also be designed to uniformly distribute its internal stress in order to minimize clamping force variations due to thermal expansions. Similarly, to facilitate installation and repair of the discs, it is important that resultant stress distribution within the clamp be relatively independent of the sequence in which the clamp screws are attached and the magnitude of the intermediate torques applied during installation.
Another drawback of many prior art disc clamps is that the screws that secure the disc clamp to the spindle hub tend to loosen as a result of thermal cycling of the drive due to stress imbalances with the clamp.
Although several suitable disc clamps have been designed in the past, effective disc clamp designs have traditionally required expensive alloys with high yield strength to accommodate the high stress concentration. However, the use of specialized alloys significantly increases production costs and fabrication complexity.
Further, one of the drawbacks of prior art disc clamps that have used screws as an attachment means is that the disc clamp is designed through an iterative process that begins with the creation of a force deflection curve and torque-deflection measurements that establish the relationship between the screw-tightening torque and the actual clamping force applied by particular disc clamps. Non-operating shock tests are performed using an actual drive to determine the minimum screw tightening torque needed to maintain the discs in place without any disc slippage.
Further, in the prior art, the use of screws creates localized point loading, thus not inherently providing equal clamping over the 360.degree. contact surface.
More recently, heat shrink clamps have been employed, wherein a sleeve is heated to a high temperature and cooled after the application of appropriate clamp load. Such a method of attachment requires custom heaters which are capable of selectively heating the clamp and the assembly process requires time to heat the clamp to the desired temperature and then cooling them back to room temperature.